[SCSI] bnx2i: Added jumbo MTU support for the no shost case

For scenarios where the shost is not being passed to bnx2i for the
iSCSI offload connection request, the code would consult the routing
table to select the CNIC device.
This code path will erroneously error out if the corresponding L2
interface's MTU has been setup to > 1500.

Signed-off-by: Eddie Wai <eddie.wai@broadcom.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>